TREATMENT OF MILK FOR MARKET 149 



however, expensive, and it has not yet been brought into practi- 

 cal use anywhere. It has hardly been tried in this country. 



The use of oxygen for disinfection has also been strongly 

 recommended. This gas, when passed in quantity into milk 

 under proper conditions, serves as a partial disinfectant. Oxygen 

 gas is, of course, perfectly harmless, and, moreover, it rapidly 

 passes off from the milk, so that it can hardly be called an 

 adulterant. Its use would, therefore, seem to offer little ob- 

 jection, if it can be found to be both practical and cheap. No 

 practical method of using it to purify a milk supply has as 

 yet been offered to the public, and none is in use at present, 

 but it offers promise for the future. 



STERILIZATION 



A few years ago it was thought that the solution of the 

 milk problem lay in destroying bacteria by heat; and there 

 developed rapidly a system of milk sterilization. This was first 

 recommended by physicians as possibly making the milk more 

 digestible by cooking, and subsequently was strongly advocated 

 by bacteriologists for destroying bacteria and rendering milk 

 .perfectly safe. 



By sterilization is meant the treatment of milk to a tem- 

 perature sufficient to destroy all bacteria. The word, however, 

 has been used in two different ways, which has given rise to 

 a slight confusion. In order to absolutely sterilize milk it is 

 necessary to use a temperature higher than that of boiling water, 

 for milk is practically sure to contain spores of bacteria that 

 cannot be killed by simple boiling. In order to destroy them 

 a temperature of 220 to 230 is necessary, and to obtain this 

 the milk must be heated in sealed chambers under steam 

 pressure. Only milk so heated can really be called sterilized, 

 and this milk is rarely found outside of a bacteriologist's labo- 

 ratory. In common use, however, the word sterilizing refers 

 to milk that has been simply boiled. The boiling of the milk 



